Add tests for git update recipe

README.rst

@@ -295,6 +295,13 @@ Let's take a look at the buildout parts directory now::
   d buildout
   d git-clone
 
+When updating, it will do a "git fetch; git reset @{upstream}"::
+
+  >>> print system(buildout)
+  Updating git-clone.
+  Fetching origin
+  HEAD is now at ...
+
 Specific branch
 ---------------
 
@@ -331,6 +338,14 @@ And let's see that current branch is "build"::
   >>> subprocess.check_output(['git', 'branch'])
   '* build\n'
 
+When updating, it will do a "git fetch; git reset build"::
+
+  >>> cd(sample_buildout)
+  >>> print system(buildout)
+  Updating git-clone.
+  Fetching origin
+  HEAD is now at ...
+
 Specific revision
 -----------------
 
@@ -369,6 +384,14 @@ And let's see that current branch is "gitclone"::
   >>> subprocess.check_output(['git', 'rev-parse', '--short', 'HEAD'])
   '2566127\n'
 
+When updating, it will do a "git fetch; git reset revision"::
+
+  >>> cd(sample_buildout)
+  >>> print system(buildout)
+  Updating git-clone.
+  Fetching origin
+  HEAD is now at ...
+
 Specific git binary
 -------------------